Roll mill

ABSTRACT

A roll mill for comminuting and homogenizing viscous masses, in particular for dispersing and uniformly distributing solid particles suspended in a binding agent. The roll mill has at least two rolls pivoted around their longitudinal axes, wherein the rotational axis of the first roll is fixed in place, and the rotational axis of a second roll is movably mounted, as well as at least one pressing device for pressing at least one roll against the other roll. Roll pressing takes place by way of a pressing device. The back roll or transfer roll intended for product removal has a shorter axial process length than the process length of the middle roll.

This application is a continuation of International Application No.PCT/CH2005/000539, filed Sep. 12, 2005, which claims priority fromGerman application 10 2004 052 084.4 filed Oct. 26, 2004, the entiredisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a roll mill, in particular to a three-rollmill, for comminuting and homogenizing viscous masses, in particular fordispersing and uniformly distributing solid particles suspended in abinding agent. Such a roll mill has at least two rolls pivoted aroundtheir longitudinal axes, wherein the rotational axis of the first rollis fixed in place, and the rotational axis of a second roll is movablymounted. At least one roll is pressed against the other by means of atleast one pressing device.

SUMMARY OF THE INVENTION

The object of the invention is to provide a roll mill of the basicdesign mentioned at the outset that enables improved product quality,while avoiding product inhomogeneities through better milling operation.

Product inhomogeneities, e.g., caused by undispersed oversize, areavoided by means of a roll mill having at least two rolls pivoted aroundtheir longitudinal axes, wherein a rotational axis of a first, middleroll is fixed in place, and a rotational axis of a second, back roll ismovable, and at least one pressing device for pressing at least one rollagainst the other roll. The back roll or transfer roll intended forproduct removal has a shorter axial process length than the middle roll,and is axially situated relative to the middle roll in such a way thatthe ends of the process length of the middle roll extend bilaterallyover the ends of the process length of the back roll or transfer roll.The advantage to this is that unabraded or only inadequately abradedproduct, i.e., excessively coarse product, does not pass from the middleroll to the back roll or transfer roll during roll mill operation.Therefore, this measure makes it possible to achieve an improved productquality, i.e., a more uniform product fineness, while avoiding undefinededge effects.

The roll surfaces or processing surfaces are preferably made out of ametal-free ceramic material, wherein the rolls preferably have a ceramiccylinder fit onto a hollow metal cylinder. This prevents the productfrom becoming metallically contaminated by roll abrasion in thecomminuting process. This is particularly important while processingpastes for applications in electronics, and for the manufacture ofinsulating bodies based on fine ceramics.

In a particularly advantageous embodiment of this invention, the rollmill according to the invention is a so-called “three-roll mill” withthree parallel rolls. The rotational axis of the middle roll is herefixed in place, while the rotational axis of the front roll or feederroll and the rotational axis of the back roll or transfer roll aremovable. To this end, it has a front mechanical-pneumatic pressingdevice for pressing the front roll against the middle roll, as well as arear mechanical-pneumatic pressing device for pressing the back rollagainst the middle roll. This provides for two roll nips. In this way,the operating conditions for both roll nips can be independentlyadjusted by setting the nip distance, the differential velocity and thepressure in the respective nip.

In another solution to the object, in particular the partial object ofan improved cooling effect, the roll mill or three-roll mill has a firstplane, which is defined by the rotational axis of the front roll orfeeder roll, and by the rotational axis of the middle roll, and a secondplane, which is defined by the rotational axis of the middle roll and bythe rotational axis of the back roll or transfer roll, both of which areinclined relative to each other by an angle of between about 10° and amaximum 90°, wherein in particular the first plane runs horizontally,while the second plane runs upwardly inclined (L-shaped roll arrangementviewed from the side). The angle preferably measures 30° to 60°, withapprox. 45° being especially preferred. As a result, the product presentas a viscous mass with the solid particles (e.g., pigments) distributedtherein is cooled for a longer period of time while passing through theroll mill than in an arrangement in which the rotational axes of thefront, middle and back roll lie in a single plane.

Such an arrangement results in a greater retention time of the producton the cool surface of the rolls.

The rolls are best cooled from the inside. For example, this isimportant while processing organic pigments, in particular with respectto certain yellow pigments.

Preferably, both the front roll and the back roll are pressed againstthe middle roll by means of a mechanical-pneumatic pressing device. Thismakes it possible to adjust the front and back roll nip. Themechanical-pneumatic pressing device preferably has a control means forsetting the nip. Since the force transducer, as explained above, enablesa “force transmission” and “path reduction”, the relatively weak forceof a pneumatic device can be multiplied for purposes of roll pressing,while at the same time greatly increasing the accuracy of nip adjustmentprescribed by the pneumatic device.

The transfer roll is best abutted by a stripper that strips away thecomminuted, homogenized mass, wherein the stripper also preferablyconsists of a metal-free material, in particular of a ceramic materialor polymer material. This also prevents the product from becomingmetallically contaminated in any way as the result of stripper abrasionwhile being stripped from the transfer roll.

A tarpaulin preferably covers at least the feed area of the roll mill.This prevents undesired contaminants from the factory building fromgetting into the product and vice versa, i.e., undesired volatileproduct constituents form getting into the air of the factory building.This improves “product hygiene” on the one hand, and “workplace hygiene”on the other.

The space under the tarpaulin is preferably connected with a gas vent.This makes it possible to keep volatile substances contained in theproduct solvent from getting into the air of a factory building.

BRIEF DESCRIPTION OF THE INVENTION

Additional advantages, features and possible applications of theinvention may be gleaned from the following description of exemplaryembodiments of the invention, which are not to be regarded as limitingin any way, wherein:

FIG. 1 shows a diagrammatic side view of a first exemplary embodiment ofthe roll mill according to the invention;

FIG. 2 shows a top view of the rolls in the first exemplary embodimenton FIG. 1;

FIG. 3 shows a diagrammatic side view of a second exemplary embodimentcorresponding to FIG. 1, and

FIG. 4 shows a top view of the rolls of the second exemplary embodimenton FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 and FIG. 2 show a first exemplary embodiment of the roll millaccording to the invention. The three-roll mill shown here containsthree rolls 1, 2, 3, which are aligned parallel to each other, and allarranged in a single plane E. In other words, the rotational axis A1 ofthe front roll 1, the rotational axis A2 of the middle roll 2, and therotational axis A3 of the back roll 3 are parallel to each other (seeFIG. 2), and all lie in one and the same plane E. In the operating mode,the front roll 1 and the back roll 3 are each pressed by a frontpressing device 4 or a back pressing device 5 against the middle roll 2,the rotational axis A2 of which is fixed in place. The front roll 1 andback roll 3 are movable, i.e., their rotational axes A1 and A3 can bepivoted around a swiveling axis D3. The jacket surfaces of rolls 1, 2, 3each comprise the roll processing surface S1, S2, S3, with which theproduct to be processed comes into contact. During operation, theproduct passing between the rolls 1 and 2 pressed against each othercreates a roll nip between the processing surface S1 of the front roll 1and the processing surface S2 of the middle roll 2. In like manner, theproduct passing between the rollers 2 and 3 pressed against each othercreates a roll nip during operation between the processing surface S3 ofthe back roll 3 and the processing surface S2 of the middle roll.

The front pressing device 4 and back pressing device 5 each have a forcetransducer 6 and a pneumatic drive 7. In the first exemplary embodimentshown on FIG. 1, the force transducer is a toggle mechanism 6, whichconsists of a first lever 6A and a second lever 6B, while the pneumaticdrive 7 consists of a pneumatic cylinder 7A and a pneumatic piston. Theforce exerted by the pressing devices 4 and 5 flows from the pneumaticpiston 7B, which is accommodated in the pneumatic cylinder 7A, andlinked with the first lever 6A on an articulated axis D1 by means of apiston rod 7B. The first lever 6A is hinged to a second articulated axisD2 on the second lever 6B, which in turn is hinged to a pivoting axisD3, and forms a respective suspension and mounting arrangement for thefront roll 1 and back roll 3.

Depending on how the levers 6A and 6B are dimensioned and oriented, thetoggle mechanism 6A, 6B used as the force transducer 6 and rollsuspension unit increase the pneumatic force of the pneumatic drive 7 bya factor of about 20 to 50, wherein this increased force is used forpurposes of roll pressing. This enables a sufficiently strong rollpressing, even with a pneumatic drive 7. On the other hand, this forcetransducer 6 decreases the stroke traversed by the pneumatic drive 7 bya factor of about 1/50 to 1/20, wherein this reduced stroke is used toset the nip.

Rolls 1, 2 and 3 are driven by overdrives or gearboxes by engine M. Theroll block 1, 2, 3 and engine block M are enveloped by a casing G.

FIG. 2 shows a top view of the rolls 1, 2, 3 of the first exemplaryembodiment of the roll mill according to the invention shown on FIG. 1.As evident, the front roll or feeder roll 1 and the middle roll 2 bothhave the same processing length L1=L2, while the back roll or transferroll 3 has a distinctly shorter processing length L3<L2 to avoidundefined edge effects. The back roll 3 is axially arranged relative tothe middle roll 2 in such a way that the ends of the processing lengthL2 of the middle roll 2 extend axially over the ends of the processlength L3 of the back roll 3 on both sides. This ensures that unabradedor only inadequately abraded product does not pass from the middle roll2 to the back roll 3 during roll mill operation, making it possible toachieve a distinctly improved product quality.

FIG. 3 and FIG. 4 show a second exemplary embodiment of the roll millaccording to the invention.

All elements of the second exemplary embodiment shown on FIG. 3 and FIG.4 that are identical to the elements of the first exemplary embodimentshown on FIG. 1 and FIG. 2 or correspond thereto bear the referencenumbers of the corresponding element from FIG. 1 or FIG. 2 with a quotemark added. How these elements of the second exemplary embodiment workwill not be explained again here. In addition the front pressing device4′ and the back pressing device 5′ with their respective forcetransducer 6′ and pneumatic drive 7′ are shown only diagrammatically.

The other reference numbers on FIG. 3 and FIG. 4 that show elements ofthe second exemplary embodiment that deviate from the first exemplaryembodiment do not bear the quote mark. Their function and importancewill be explained below.

The essential difference between the first exemplary embodiment (FIG. 1and FIG. 2) and the second exemplary embodiment (FIG. 3 and FIG. 4) isthat the three-roll mill depicted here has three rolls 1′, 2′, 3′ which,while aligned parallel to each other, are not all arranged in the sameplane. Rather, the rotational axis A1′ of the front roll 1′ and therotational axis A2′ of the middle roll 2′ are arranged in a first planeE1, while the rotational axis A3′ of the back roll 3′ and the rotationalaxis A2′ of the middle roll 2′ are arranged in a second plane E2 thatforms an angle y of about 45° relative to the first plane E1. As aresult of arranging the three rolls 1′, 2′, 3′ in this way, the productpresent as a viscous mass with the solid particles (e.g., pigments)distributed therein can be cooled for a longer period of time, and hencemore intensively, than in an arrangement in which the rotational axes ofthe front, middle and back roll lie in a single plane.

FIG. 4 is a top view of the rolls 1′, 2′, 3′ of the second embodiment ofthe roll mill according to the invention shown on FIG. 3. Here as well,the front roll or feeder roll 1′ and middle roll 2′ both have the sameprocessing length L1′=L2′, while the back roll or transfer roll 3′ has adistinctly shorter processing length L3′<L2′. The back roll 3′ is alsoaxially arranged relative to the middle roll 2′ in such a way that theends of the processing length L2′ of the middle roll 2′ extend axiallyover the ends of the processing length L3′ of the back wall 3′ on bothsides. As already explained, this ensures that no unabraded or onlyinadequately abraded product gets from the middle roll 2′ to the backroll 3′ during operation of the three-roll mill, thereby improvingproduct quality.

The path traversed by the product as it passes through the roll millaccording to the second exemplary embodiment is increased by the twoadditional circular arc lengths at the surfaces S2′ and S3′ of the roll2′ and 3′ with radius R that arise between plane E1 and plane E2 as theresult of angle δ, i.e., an additional path relative to the firstexemplary embodiment (FIG. 1) by 2×δ×R.

A transfer funnel or product trough 8 with stacking wedges extendingfrom the introduction region on either side is arranged over the area ofthe introduction nip between the front roll 1′ and the middle roll 2′.As the result of the stacking wedges provided in addition to theconventional wedge gaskets, this product trough increases tightness,thereby ensuring a lower lateral product loss.

A stripper 9 with a stripping knife is used for removing the productfrom the back roll 3′. The stripper 9 is equipped with an automaticknife adjustment, which is actuated from an SPS controller.

In both the first and second exemplary embodiment, the roll surfaces orroll processing surfaces S1, S2, S3 or S1′, S2′, S3′ can be made out ofceramic material. The stripper 9 shown on FIG. 3 can also consist ofceramic material or polymer material. These or other metal-freematerials for the roll processing surfaces and the stripper knife are ofparticular interest for processing pastes in the electronics industry.

The ceramic rolls are rounded at the end of the roll processing length.

The pneumatic drive 7 operates at pressures of up to 4 bar, for example,which are brought to bear via the force transducers 6 on the requiredline pressures in the roll nips. The force transducer 6 make sitpossible to increase the pressing force exerted on the rolls by the rollpressing devices 4, 5 by a factor of about 10 to about 80. Accordingly,the reduction in the stroke prescribed by the pneumatic drive 7 via theforce transducer increase the nip setting accuracy by the same factor.

The rolls have a diameter of 300 mm, and the back roll 3, 3′ is about 4mm to 5 mm shorter than the middle roll 2, 2′. As a result, the stripper9 only strips abraded product from the back roll 3′.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited but by thespecific disclosure herein, but only by the appended claims.

1. A roll mill for comminuting and homogenizing viscous masses,comprising: at least two rolls pivoted around their longitudinal axes,wherein a rotational axis of a first, middle roll is fixed in place, anda rotational axis of a second, back roll is movable; and at least onepressing device for pressing at least one roll against the other roll,wherein in the back roll used for product removal has a shorter axialprocessing length than a processing length of the middle roll, the backroll being axially situated relative to the middle roll so that ends ofthe processing length of the middle roll extend over the ends of theprocessing length of the back roll on both sides.
 2. The roll millaccording to claim 1, wherein the rolls have surfaces made out of ametal-free ceramic material.
 3. The roll mill according to claim 1,wherein the mill is a three-roll mill, and the rolls are arranged, whenviewed from the side, in the form of an L.
 4. The roll mill according toclaim 1, wherein in the rolls have a ceramic cylinder fit onto a hollowmetal cylinder.
 5. The roll mill according to claim 1, wherein the rollsare internally cooled.
 6. The roll mill according to claim 1, whereinthe pressing device is a mechanical-pneumatic pressing device.
 7. Theroll mill according to claim 1, wherein the pressing device has acontroller for setting the nip.
 8. The roll mill according to claim 1,wherein the back roll is 2 mm to 10 mm shorter than the middle roll. 9.The roll mill according to claim 8, wherein the back roll is 3 mm to 6mm shorter than the middle roll.